1. Field of the Invention
The present invention pertains to a heat exchanger unit particularly adapted for gas fired hot air furnaces wherein two pan shaped sections are joined together along cooperating flanges which are folded one over the other and crimped tightly to form a substantially leakproof joint.
2. Background
In the development of so called clamshell type heat exchanger units certain improvements have been made wherein a seam is sealed by folding a flange portion of one shell section over a cooperating flange of the other shell section and crimping the folded flanges to securely lock the sections together and prevent undesirable relative movement during the cyclical heating and cooling of the heat exchanger unit. Although the inventions disclosed and claimed in the above referenced application and patent comprise a significant improvement in shell type heat exchanger units the further development of the inventive concept has included the desideratum of achieving a more consistent seal around the edges of the clamshell sections. The formation of a substantially gas-tight seal at the seam between the sections of a clamshell type heat exchanger is, of course, important with respect to preventing the leakage of combustion products during normal operating conditions from the interior of the heat exchanger into the plenum through which conditioned air is being circulated. On the other hand, under certain operating conditions it may be desirable to have a seam which will temporarily yield to excessive pressure within the interior of the heat exchanger to release gases to reduce the pressure without undergoing a catastrophic failure of the heat exchanger itself. Accordingly, it is a primary object of the present invention to provide a clamshell type heat exchanger having opposed pan shaped sections, each formed with a peripheral flange, which are joined together and formed into a unitary structure by folding one flange over the other to form a substantially gas-tight or leakproof seal. This objective has been met by the invention described and claimed herein.